Decoding synaptic imbalance in neurodegenerative diseases: From pathological analysis to targeted intervention.

Synapses serve as the central functional components mediating information transmission, integration, and storage within the central nervous system (CNS). Their functionality depends on the synergistic interplay of the presynaptic membrane, synaptic cleft, and postsynaptic membrane-three structures that collectively sustain neurotransmitter secretion, postsynaptic signaling, and synaptic plasticity. Of note, synaptic impairment represents an early, shared pathological hallmark across aging and age-related neurodegenerative disorders like Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and Amyotrophic lateral sclerosis (ALS). This damage emerges prior to the demise of neuronal cell bodies and the manifestation of clinical symptoms, with its location and severity directly shaping disease phenotypes. Importantly, such synaptic dysfunction is closely linked to the pathological proteins specific to each disorder. This review comprehensively synthesizes current research advances regarding synaptic impairment in age-related neurodegenerative diseases. It elaborates on the location-specific pathological features of synaptic damage in AD, PD, HD, and ALS, with particular emphasis on their associations with disease-related pathological markers. Additionally, the work unpacks five core mechanisms driving synaptic dysfunction: the toxic effects of pathological proteins, dysregulated synaptic protein homeostasis, excitotoxicity coupled with disrupted calcium balance, oxidative stress and inflammatory responses, and deficiencies in neurotrophic factors. Ultimately, it summarizes potential biomarkers and targeted intervention strategies, aiming to provide a systematic reference for mechanistic investigations, early diagnosis, and clinical management of neurodegenerative diseases.